Voltage control sensor and control interface for radio frequency power regulation in a plasma reactor

ABSTRACT

A plasma reactor system with controlled DC bias for manufacturing semiconductor wafers and the like. The reactor system includes a plasma chamber, a plasma generating coil and a chuck including a chuck electrode. The chuck supports a workpiece within the chamber. The plasma reactor system further includes a pair of generators, one of which supplies a radio frequency signal to the plasma generating coil. The second generator delivers a RF signal which to the chuck electrode and acts to control DC bias at the workpiece. Peak voltage sensor circuitry and set point signal circuitry controls the power output of the generator, and a matching network coupled between the generator and the first electrode matches the impedance of the RF signal with the load applied by the plasma. DC bias determines the energy with which plasma particles impact the surface of a workpiece and thereby determines the rate at which the process is performed. This DC bias forms at the surface of the workpiece upon generation of a plasma in the plasma chamber and is affected by the RF signal applied to the chuck electrode. Since power losses within the match network are variable and unpredictable, the peak voltage at the electrode can not be consistently maintained by simply applying a predetermined generator output. By monitoring the peak voltage at the electrode and generating a corresponding control signal to control the generator, a consistent DC bias and corresponding process rate can be maintained.

This is a continuation of Ser. No. 09/410,183, filed Sep. 30, 1999, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plasma processing systems and, moreparticularly, to methods and apparatus for controlling radio frequencydelivery in a plasma reactor through monitoring and feedback of anelectrical parameter, in particular a peak voltage.

2. Background Art

Ionized gas, or plasma, is commonly used during the processing andfabrication of semiconductor devices. For example, plasma can be used toetch or remove material from semiconductor integrated circuit wafers,and to sputter or deposit material onto semiconducting, conducting orinsulating surfaces.

With reference to FIG. 1A, creating a plasma for use in manufacturing orfabrication processes typically begins by introducing various processgases into a plasma chamber 10 of a plasma reactor, generally designated12. These gases enter the chamber 10 through an inlet 13 and exitthrough an outlet 15. A workpiece 14, such as an integrated circuitwafer is disposed in the chamber 10 held upon a chuck 16. The reactor 12also includes plasma density production mechanism 18 (e.g. a TCP coil).A plasma inducing signal, supplied by a plasma inducing power supply 20is applied to the plasma density production mechanism 18. the plasmainducing signal is preferably a radio frequency (RF) signal. Adielectric window 22, constructed of a material such as ceramic,incorporated into the upper surface of the chamber 10 allows efficienttransmission of the first RF signal from the TCP coil 18 to the interiorof the grounded chamber 10. This first RF signal excites the gasmolecules within the chamber, generating a plasma 24.

The plasma 24 formed within the chamber 10 includes electrons andpositively charged particles. The electrons, being lighter than thepositively charged particles tend to migrate more readily, causing asheath to form at the surfaces of the chamber 10. A self biasing effectcauses a net negative charge at the inner surfaces of the chamber. Thisnet negative charge, or D.C. sheath potential acts to attract theheavier positively charged particles toward the wall surfaces. Thestrength of this D.C. bias in the location of the workpiece 14 largelydetermines the energy with which the positively charged particles willstrike the workpiece 14 and correspondingly affects the desired process(e.g. etch rate, or deposition rate).

The present invention will be more readily understood by bearing in mindthe distinction between DC bias and DC sheath potential. DC bias isdefined as the difference in electrical potential between a surfacewithin the chamber 10 and ground. DC sheath, on the other hand isdefined as the difference between the plasma potential and the potentialof a surface within the chamber as measured across the plasma sheath.

The workpiece is held upon a chuck 16 is located at the bottom of thechamber 10 and constitutes a chuck electrode 26. A bias RF power source28 supplies a biasing RF signal to the chuck electrode 16.Alternatively, in some systems the both the plasma density signal andbias signal are in fact a single signal produced by a single powersource.

This second excitation signal, preferably in the form of a RF signal, atthe second electrode increases the DC bias at the location of theworkpiece, depending on the disposition of the RF electric field withinthe chamber 10, and this increases the energy with which the chargedparticles strike the workpiece. Variations in the RF signal supplied tothe second electrode 16 produce corresponding variations in the D.C.bias at the workpiece affecting the process.

With continued reference to FIG. 1A, the bias RF power source 28described above supplies a R.F. signal to the chuck electrode 26. Thissignal passes through a match network 30 disposed between the bias RFpower source 28 and the chuck electrode 26. The match network 30 matchesthe impedance of the RF signal with the load exhibited by the plasma. Asimilar match network 31 is provided between the power inducing powersource 20 and the TCP coil 18. As discussed above, the control anddelivery of the RF signal at the chuck electrode 26 is of fundamentalimportance in plasma processing. Significant variance in actual powerdelivered may unexpectedly change the rate of the process.Unfortunately, the match network 30 generates significant losses in theRF signal. Furthermore, these losses are variable and, to a degree,unpredictable. Therefore, simply supplying a predetermined RF signalpower from the RF power source 28 does not ensure that a predictable andconsistent RF signal will be delivered at the electrode 26.

With continued reference to FIG. 1A, one method which has been used toattach the workpiece 14 to the chuck 16 has been to provide the chuckwith clamps 32 which contact the surface of the workpiece along itsedges to hold the workpiece to the chuck. Using such a chuck 16 (and tothe extent that the workpiece is somewhat conductive) it is possible tomeasure the D.C. bias directly by installing a pickup 33 at theelectrode 26 and transmitting a voltage signal to a voltage sensor 34.The power source could then be feedback controlled to maintain aconstant measured D.C. bias. However, using such clamps 32 to attach theworkpiece 14 to the chuck 16 presents multiple problems. For one,valuable surface area may be wasted on the workpiece due to itsengagement with the clamps 32. In addition, any such contact of clamps32 to the workpiece 14 is undesirable due the risk of damage to theworkpiece 14, and the generation of particles.

With reference to FIG. 1B, another method which has been used to holdthe workpiece onto the electrode has been to provide an electrode in theform of an electrostatic chuck 36. In its most general sense anelectrostatic chuck includes an electrode 38 which is covered with aninsulator 40. The electrically conductive workpiece 14, which isgenerally semiconductive, sits on the electrically insulating material.When a DC voltage is applied to the electrode 38, the electrode andworkpiece 14 become capacitively coupled resulting in oppositeelectrical charges on each, attracting the workpiece 14 and electrode 38toward one another. This acts to hold the workpiece against the chuck36.

More particularly, the electrostatic chuck 36 can be understood withreference to FIG. 1C in addition to FIG. 1B. In this bipolarimplementation, the electrode 38 of the electrostatic chuck 36 includesfirst and second electrically conducive portions 42 and 44, which areelectrically isolated from one another. A DC voltage from a D.C. voltagesource 46, passes through a filter 47 before being applied between thefirst and second portions 42 and 44 of the electrode 38. This causes thedesired electrostatic attraction between the electrode 38 and theworkpiece 14, thereby holding the workpiece to the chuck 36.

With reference to FIG. 1D, a simpler version of electrostatic chuck isillustrated. This simpler form of electrostatic chuck, termed a monopolar chuck 37 is shown in plan view in 1D. By applying a DC potentialbetween the workpiece 14 and the chuck an electrostatic charge on eachholds the workpiece to the chuck. It will be appreciated by thoseskilled in the art that numerous other forms of electrostatic chuck arepossible as well.

However, use of such an electrostatic chuck 36 renders a directmeasurement of the D.C. bias at the workpiece impractical. End users areaverse to having their sensitive semiconductor products touched by anymechanical probe or electrically conductive item such as a voltagesensor. In addition, it would be difficult to maintain sensor accuracyand longevity in the plasma environment. Correlating the D.C. voltage bymeasuring the power of the RF signal at the electrode 16 is alsodifficult and does not provide an accurate measurement of the D.C.sheath potential due, in part, to the capacitive coupling between theelectrode and the workpiece.

Therefore, there remains a need for system for controlling R.F. power atan electrode to maintain a consistent D.C. sheath potential. Such asystem would preferably not involve contact with a workpiece, would notrequire placing a sensor with the plasma environment of the plasmachamber, and would account for variable and unpredictable power lossesthrough a match network.

SUMMARY OF THE INVENTION

The present invention provides a plasma reactor having a chamber and achuck supporting a workpiece within the chamber. The chuck includes achuck electrode which receives a bias radio frequency (RF) signal from abias RF power source. The RF signal at the electrode affects the plasma,and more particularly affects the DC bias. A sensor measures a parameterof the plasma, such as for example the peak voltage of the RF signaldelivered to the electrode which is compared with the desired set pointand from which an error signal is derived. The error signal is thenamplified and used to control the RF power source.

Typically, a match network, located between the bias RF power source andthe chuck, matches the impedance of the plasma load to that of theoutput (typically 50 Ohms) of the RF power source. The maintenance of aconsistent RF signal at the electrode is of importance in maintaining aconsistent DC bias at the workpiece and a correspondingly consistentprocess. For instance the RF delivery system is subject to losses suchthat process results may not be predictable and constant. For example,the match network generates substantial power losses in the RF signal,these losses being variable and, to an extent, unpredictable. By sensingthe RF peak voltage near the electrode and using that sensed voltage togenerate a corresponding error signal to control the power supply, aconsistent D.C. bias can be maintained at the workpiece in spite of thevariation in transmission, such as for example those generated by thematch network.

More particularly, the present invention is preferably embodied in aninductive plasma reactor having a Transformer Coupled Plasma (TCP)reactor coil. This coil can be located outside of the plasma chamber andis separated from the plasma by a ceramic window, provided in wall ofthe chamber. A plasma generating RF source supplies a RF signal to theTCP coil. A gas flows through the chamber, and is ionized by RF currentinduced from the TCP coil. The RF current is coupled to the plasmaprimarily by magnetic induction through a dielectric window. Thefundamental purpose of the TCP coil and the signal supplied thereto isto generate plasma density.

As the plasma is formed, the electrons, which tend to migrate moreeasily than the positive ions, develop a net negative charge on the atthe inner surfaces of the chamber as well as at the workpiece supportedupon the chuck. This net charge generates a DC bias which determines theenergy with which the positively charged particles strike the surface ofthe workpiece and thereby is a primary factor in determining the processresults.

A pickup connected to the electrode receives the RF signal delivered tothe electrode. This signal is then passed through a lead wire to the RFsensor which is located as close to the chuck electrode as is possiblewithout risking arcing between the sensor and the chuck electrode.Placing the sensor close to the electrod minimizes the length of leadwire necessary to transmit the RF signal to the sensor, therebyminimizing inductive and resistive affects of the lead wire upon thesignal.

Within the sensor, the RF signal is divided and separated into AC and DCcomponents. If desired, the DC component can be used to monitorelectrostatic chuck function. However that is not a necessary componentof the present invention. The AC signal component then passes through asurge protection circuit before being fed to a balanced detectorcircuit. The balanced circuit ensures that the AC signal issymmetrically loaded about the zero volt axis, ensuring that the signaldoes not generate a spurious DC component which would induce error intothe system. The AC signal is then passed through an amplifier circuitwhich includes a feedback circuit and incorporating retification andpeak hold circuitry to yield a DC equivalent of the RF peak voltage.Matched diodes in both arms of the amplifier circuit, together with thediode in the balance circuit, ensure that any non-linearity is largelycompensated or in the DC equivalent signal at the output of theamplifier.

This DC equivalent signal is then passed through a differential bufferand an amplifier with gain and offset adjustment before being deliveredas an output signal. This same signal is then compared with the desiredsetpoint to derive an error signal which is passed through a high gainamp and through a power limit circuit which protects the electrode frombeing damaged by a surge. The signal passes to the generator to providea RF generator as a command to control the power produced.

Alternatively the present invention can be used with a capacitivelycoupled plasma reactor. In such an electrode capacitively coupled withthe chuck electrode replaces the TCP coil described above. In addition,the present invention can be used with a mechanical chuck rather than anelectrostatic chuck obviating the need to place a sensor within theplasma environment.

By detecting the RF peak voltage delivered at the electrode, the presentinvention accurately and efficiently controls the RF signal delivered tothe chuck elecrode, allowing a consistent DC bias to be maintained. Inthis way, the plasma reactor can consistently produce high qualityuniform workpieces.

While the invention has been described in terms of using RF peakvoltages delivered to the electrode, it should be appreciated that otherprocess parameters can be monitored as well and used in a feedbacksystem to control the process. By way of example, the current suppliedto the coil could be monitored and used in a feedback system.

These and other advantages of the present invention will become apparentto those skilled in the art upon a reading of the following descriptionsof the invention and a study of the several figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, withlike reference numerals designating like elements.

FIG. 1A is a schematic diagram of a plasma reactor system of the priorart;

FIG. 1B is a schematic diagram of another plasma reactor of the priorart;

FIG. 1C is an expanded view, taken from line 1C—1C of FIG. 1B, of anelectrostatic chuck of the prior art;

FIG. 2A is a schematic view of a plasma reactor system of the presentinvention;

FIG. 2B is a view, shown enlarged, taken from area 2B of FIG. 2A;

FIG. 3 is a schematic of circuitry within sensor 210 of FIG. 2B;

FIG. 4 is a view taken from area 4 of FIG. 2B of the present inventionin calibration mode;

FIG. 5 is a process diagram of a method of calibrating the plasmareactor of the present invention and;

FIG. 6 is a process diagram of a method of controlling RF signalgeneration according to the present invention

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

FIGS. 1A, 1B and 1C have been discussed with reference to the backgroundart.

With reference to FIG. 2A, the present invention is embodied in a plasmareactor system, generally referred to as 200. The plasma reactor 200includes a plasma chamber 202 and a Transformer Coupled Plasma (TCP)coil 204 disposed outside and above the plasma chamber 202. The plasmachamber 202 further includes a gas inlet 203 and a gas outlet 205. TheTCP coil 204 is coupled with a plasma generation power source 206 whichprovides a plasma generating Radio Frequency (RF) signal. A matchnetwork 207 is included between the plasma generation power source 206and the TCP coil 204. A ceramic window 208 located adjacent the TCP coil204 in the upper wall of the chamber 202 allows efficient transmissionof the plasma generating RF signal into the plasma chamber 202. Anelectrostatic chuck 210, located at the bottom of the chamber 202,supports a workpiece 212.

With continued reference to FIG. 2A, the electrostatic chuck includes achuck electrode 214. The chuck electrode 214 includes a first and secondelectrically conductive portions 216 a and 216 b which are electricallyisolated from one another. The chuck electrode 214 is surrounded by anelectrical insulator 217. By applying a DC voltage across the conductiveportions, as discussed in the prior art, an electrostatic coupling iscreated between the portions 216 a and 216 b and the workpiece 212. Thiscoupling attracts the workpiece 212 holding it fast against the chuck210.

A bias RF power source 218 is coupled with a match network 220 which isfurther coupled with the chuck electrode 214. A pickup 222 extends intothe chuck 210 electrically connecting with the chuck electrode 214. Thispickup 222 is coupled via a lead wire 224 with a RF peak voltage sensor226. This RF peak voltage sensor generates a monitor signal which iscombined with the set point in summing circuitry 228 to generate acontrol signal which may optionally then be used to control the biasgenerating power source 218.

In operation, a gas capable of ionization flows into the chamber 202through the gas inlet 203 and exits the chamber through the gas outlet205. A plasma generating RF signal is produced by the RF power source206 and is delivered to the TCP coil 204. This plasma generating RFsignal radiates from the coil 204 through the window 208 and into thechamber 202, where it causes the gas within the chamber 202 to ionizeand form a plasma 230 within the chamber.

With further reference to FIG. 2A, the plasma produces a sheath 232along the walls of the chamber 202. The plasma generated within thechamber 202 includes electrons and positively charged particles. Theelectrons, being much lighter than the positively charged ions, tend tomigrate more readily, generating a DC sheath potential at the surfacesof the chamber 202. This sheath potential being negative tends toattract the positively charged ions and repels further electrons, thuscontaining them. The average DC sheath potential at the location of theworkpiece 212 predominantly determines the energy with which thepositively ions strike the workpiece, and therefore a primarydeterminant of process parameters. For instance it will affect the rateat which etching or deposition take place.

The amount of DC bias at the workpiece, and corresponding processconditions, can be altered, e.g. the rate increased, by applying an RFsignal to the chuck electrode. To this end, a RF signal is generated bythe RF power source 218. This RF signal passes then passes through thematch network 220 which matches the impedance of the RF generator,typically 50Ω, to that presented by the plasma load 230. This matchedsignal then passes to the chuck electrode 214, which being capacitivelycoupled with the workpiece, passes the signal to the workpiece throughthe insulator 217 of the chuck 210.

With continued reference to FIG. 2A, substantial power losses may occuras the signal passes through the match network 220. Furthermore, asdiscussed in the Background of the Invention, these losses are variableand difficult to predict. In order to account for these variable andunpredictable power losses the pickup 222 collects the peak voltage ofthe RF signal at the chuck electrode and passes this voltage to thevoltage sensor 226 through the lead wire 224. With reference to FIG. 2Bthe length of the lead wire should be as short as possible to minimizeinductive and resistive effects on the transmission of the pickupsignal, while at the same time providing sufficient distance “d” betweenthe sensor 226 and the chuck 210 to prevent electrical arcing betweenthe chuck and the sensor.

With reference to FIG. 3, the sensor circuitry 226 receives the RFsignal from the lead wire 224 at an input 302. The sensor circuitry 226contains both a DC divider for ESC clamp monitoring (unrelated to thepresent invention) and a separate AC divider with clamp protectioncircuitry 304 whose output is a fraction of the incoming RF, which isthen sent on to a balancing circuit 306. The balancing circuit ensuresthat the RF signal is symmetrically balanced about the zero volt axis,preventing DC offset errors from being introduced into the system. Thebalanced ac signal is then passed to an amplifier circuit 308 whichincludes rectification and feedback circuitry which converts the RFsignal into a DC signal equivalent to the RF peak value. Matched diodes,309 a, 309 b and 309 c, are included in the balancing/rectificationcircuit 306 and feedback loop of the amplifier circuit 308. The matcheddiodes 309 a and 309 b are manufactured on the same chip to have exactlythe same performance characteristics as one another, and with 309 c, actto ensure that any losses in the balance circuit will not affect the DCsignal produced by the amplifier circuit 308.

The DC monitor signal produced by the sensor circuitry provides anaccurate indication of the RF peak value at the electrode 214. Withcontinuing reference to FIG. 3, this DC monitor signal then is passed toa differential ground compensating buffer amplifier 314 and then througha gain and offset adjustment stage 316 which outputs a DC signal 319suitably scaled representing the RF peak value at the electrode 214.This DC output signal 319 is summed in appropriate phase with a DC setpoint command signal 330, thus generating an error signal for feedbackcontrol 318. The control signal 318 then passes through a high gain amp320 and a power limit circuit 322. The power limit circuit preventsdamage to the system by preventing a power-surge when the bias powersource 218 is switched to voltage control, or whenever the voltagecontrol loop becomes incomplete for any reason. The signal then passesthrough a final filter/buffer amp 324 and then to the power source 218in the form of a RF generator command signal. A series relay controlledswitch 328 allows the generator command signal 326 to be controlledeither by the feedback circuitry as described or by using the commandsignal 330 as a simple power set point if desired.

With reference to FIG. 6, the circuitry 226 operates according to aprocess 600, which begins with a step 602 of detecting a peak RFvoltage. Then, in a step 604, the DC representation of the RF peakvoltage signal is processed for ground restoration, gain and offset toyield a monitor signal 319. In a step 606 the monitor signal 319 issummed in appropriate phase with a command setpoint signal 330, togenerate an error signal 318. In a step 607, the error signal 318 isfurther amplified and then limited to a safe level for output as thegenerator command signal. Finally, in a step 608, after selection ofdirect power or voltage feedback mode, the power source 218 is drivenaccording to the direct or modified command signal respectively. Asillustrated in FIG. 6, the method 600 when conducted in a negative feedback control fashion acts to maintain a desired sensed parameter, inthis instance peak RF voltage applied at the chuck.

With reference to FIGS. 4 and 5, in order to determine the relationshipbetween bias voltage at the workpiece 212 and the peak voltage of thedelivered signal, the plasma reactor system 200 must first becalibrated. FIG. 5, illustrates a process 500 for calibrating thereactor system 200. The process 500 begins with a step 502 in which aworkpiece is placed into the chamber in the usual manner. The wafer usedfor calibration should be expendable, somewhat conductive and notintended for production, for reasons which will become apparent. In astep 504, an electrical probe 402 (FIG. 4) is engaged to the uppersurface of the workpiece 212. Attaching the probe directly to the uppersurface of the workpiece allows a direct measurement of the RF inducedDC self bias during operation of the plasma reactor 200. However, directcontact with the upper surface of the workpiece risks damaging thesemiconductor workpiece, and for this reason the workpiece used shouldonly be intended for calibration and not for production. Then, in a step506, a plasma process is run, during which a DC bias will form at theworkpiece 212. This DC bias can then be directly measured as detected bythe probe, and correlated to the RF peak voltage measured as detectedfrom the pickup 222. Then, in a step 508, the DC bias and RF peak valuescan be compared at several power settings and a relationship therebetween can be determined. Finally in a step 510, the plasma reactorsystem 200 is calibrated.

In use, the plasma reactor 200 can be set for automatic adjustment bygenerating an error signal 318 with sufficient amplification throughamplifier 320, to maintain RF peak voltage at the electrode 214, bycontinuously adjusting the output of RF power source 218.

In an alternate embodiment of the invention, not shown, the plasmareactor uses capacitively coupled electrodes to generate a plasma withinthe chamber. This embodiment of the invention operates substantiallysimilarly to the above described embodiment by detecting a peak RFvoltage of a bias RF signal at a chuck electrode and feeding back asignal to the bias generating RF power source to control the bias RFsignal. Similarly, with a suitable sensor another parameter such asdelivered current or power could be chosen as the control parameter inthe feedback scheme, although the relationship to the sheath bias wouldbe different. In particular, the real part of the current would berelated to plasma density.

In yet another embodiment of the invention, also not shown, a mechanicalchuck holds the workpiece using clamps as described in the background ofthe invention. Again this embodiment of the invention would operatesubstantially similarly to the above described embodiments to maintainconsistent plasma parameters by monitoring peak RF voltage at the chuckelectrode and feeding back a control signal to the bias RF power source.

In summary, the present invention provides an effective and accurate wayto perform a plasma process with a consistent and predicable DC bias.This consistent DC bias ensures that process parameters such as etchrate are predictable and consistent, resulting in higher qualitysemiconductor wafers and increased production yield.

While the invention has been described herein in terms of a preferredembodiment, other embodiments of the invention, including alternatives,modifications, permutations and equivalents of the embodiments describedherein, will be apparent to those skilled in the art from considerationof the specification, study of the drawings, and practice of theinvention. The embodiments and preferred features described above shouldbe considered exemplary, with the invention being defined by theappended claims, which therefore include all such alternatives,modifications, permutations and equivalents as fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A plasma reactor system for use in the processingand manufacture of a workpiece, the plasma reactor system comprising: aplasma chamber for containing a plasma therein and having an interiorconfigured for support and plasma processing of the workpiece; aworkpiece support electrode disposed at least partially within saidplasma chamber; at least one variable power source supplying anelectrical signal to said electrode; and feedback circuitry including: asensor circuit for sensing at least one parameter related to said plasmaand generating an error signal corresponding to deviations in saidparameter through use of a summing amplifier providing negative feedbackcontrol responsive to said deviations of said parameter wherein if theparameter related to said plasma is a second electrical signal, saidsecond electrical signal is detected by a pickup, said pick-up beingdisposed at least partially within said electrode.
 2. The plasma reactorof claim 1, wherein the at least one variable power source supplying anelectrical signal to said electrode includes: a first variable powersource supplying an electrical signal to said electrode, said firstpower source is capable of being the principle source bias in saidplasma; and a second variable power source, said second power sourcebeing primarily for generation of said plasma.
 3. A plasma reactor asrecited in claim 1, wherein said parameter related to said plasma is anoptical signal.
 4. A plasma reactor as recited in claim 1 wherein saidpickup is connected with said electrode.
 5. A plasma reactor as recitedin claim 1 wherein said parameter of said plasma is a power value ofsaid electrical signal supplied to said electrode.
 6. A plasma reactoras recited in claim 1 wherein said parameter of said plasma is a voltagevalue of said electrical signal supplied to said electrode.
 7. A plasmareactor as recited in claim 1 wherein said parameter of said plasma is apeak voltage value of said electrical signal supplied to said electrode.8. A plasma reactor as recited in claim 1 wherein said parameter is acurrent value of said signal supplied to said electrode.
 9. A plasmareactor as recited in claim 1 wherein said parameter is a combination ofcomplex voltage and current values of said electrical signal supplied tosaid electrode.
 10. A plasma reactor as recited in claim 1 wherein saidparameter of said plasma is a phase value of said electrical signalsupplied to said electrode.
 11. A plasma reactor as recited in claim 1wherein said electrical signal is a radio frequency signal.
 12. A plasmareactor system as recited in claim 1, wherein said electrical signal isa microwave signal.
 13. A plasma system as recited in claim 11 whereinsaid radio frequency signal induces a direct current bias voltage acrossa plasma sheath at said electrode and wherein said peak voltage sensedby said sensor correlates to said direct current bias voltage.
 14. Aplasma reactor system as recited in claim 1 wherein said sensorcircuitry is located outside of said chamber.
 15. A plasma reactorsystem as recited in claim 1 wherein said sensor circuitry is as closecoupled as possible with said pickup.
 16. A plasma reactor system asrecited in claim 1, further comprising a conduit coupled between saidpickup and said sensor circuitry to transmit said signal therebetween.17. A plasma reactor system as recited in claim 1 further comprising amatch network connected between said power source and said electrode.18. A plasma reactor system as recited in claim 17 wherein said sensorcircuitry is coupled between said match network and said electrode. 19.A plasma reactor system as recited in claim 1 wherein said chamber isconnected with and electrically insulated from said electrode.
 20. Amethod for controlling power supplied to a plasma reactor, the plasmareactor being useful in the process and manufacture of a workpiecethrough reaction with a plasma contained therein, the method comprising:generating an electrical signal; delivering said signal to at least oneelectrode within the plasma reactor; generating an error signalcorresponding to at least one parameter wherein if said at least oneparameter is a second electrical signal, said second electrical signalis detected by a pickup, said pick-up being disposed at least partiallywithin said at least one electrode; and controlling said power sourcebased upon said error signal.
 21. A method as recited in claim 20wherein said parameter includes a voltage of said electrical signal. 22.A method as recited in claim 21 wherein said parameter includes a peakvoltage of said electrical signal.
 23. A method as recited in claim 20wherein said parameter includes a power value of said electrical signal.24. A method as recited in claim 20 wherein said parameter is a phasevalue of said electrical signal.
 25. A method as recited in claim 20wherein said parameter is a current value of said electrical signal. 26.A method as recited in claim 20 wherein said parameter is a combinationof complex voltage and current of said electrical signal.
 27. A methodas recited in claim 20 wherein said parameter is an impedance of saidelectrical signal.
 28. A method as recited in claim 20 wherein saidparameter is an immittance of said electrical signal.
 29. A method asrecited in claim 20 further comprising the step of combining said errorsignal with a set point signal to generate a command signal capable ofdriving said power source.
 30. A method as recited in claim 20 furthercomprising the step of matching a load presented by the plasma with saidelectrical signal.
 31. A method as recited in claim 20 wherein saidelectrical signal is provided by a low impedance power source providinga signal which roughly matches the load presented by the plasma.
 32. Amethod as recited in claim 20 wherein said signal is a radio frequencysignal having a peak voltage and wherein said parameter is said peakvoltage of said electrical signal.
 33. A method as recited in claim 32further comprising the step of generating a plasma, said plasma creatinga DC bias which is correlated to said peak voltage of said radiofrequency signal.
 34. A method as recited in claim 22 wherein said peakvoltage is detected from a pickup located at least partially within saidelectrode.
 35. A method as recited in claim 32 wherein said step ofgenerating an error signal includes the step of generating a DC signalwhich is a valid representation of said peak voltage of said radiofrequency signal.
 36. A method as recited in claim 20 wherein said stepof controlling said power source is performed manually.
 37. A method asrecited in claim 20 wherein said step of controlling said power sourceis performed automatically.
 38. A method for controlling power suppliedto a plasma reactor, the plasma reactor being useful in the process andmanufacture of a workpiece through reaction with a plasma containedtherein, the method comprising: generating an electrical signal;supplying said electrical signal to a coil to thereby strike a plasmawithin the reactor; sensing at one parameter of said signal; generatingan error signal corresponding to at least one parameter wherein if saidat least one parameter is a second electrical signal, said secondelectrical signal is detected by a pickup, said pick-up being disposedat least partially within said at least one electrode; and controllingsaid power source based upon said error signal.
 39. A method as recitedin claim 38 wherein said parameter is a current.
 40. A method as recitedin claim 39 wherein said parameter is a voltage.
 41. A method as recitedin claim 40 wherein said parameter is a combination of complex currentand voltage.